TH350 Strength

impstocker · 12-21-2015, 11:08 AM

I am finishing up my 1965 Impala 396/325 Stocker mocking up the motor with TH350 intalled in car. In previous post I mention the tranny has been in storage since 2002, I originally going to use in the 68 Impala I ran. (ran a stick in that one)

The only thing I remember was I did get a 2.75 first gear plus a manual valve body. I don't even remember who built it except I think it was somebody in North Carolina. I finally did drop the pan last week, everything was clean (tranny has never been run) plus has a ATI valve body. I don't know if it has the 36 element sprag, but having it built they knew it was going into a race car, back then I had more $ so for now I can assume it has it. I remember it was around $900 in 2002.

I like doing my own work plus lots of info, in reading Cliff Ruggles "GM Turbo 350" book he says:
"the TH400 case is stronger where it flares up to the bellhousing area. I have seen a good number of TH350 break at this location, but all of those were being used in drag racing with high HP plus traction. Pinion angle, engine mounts (I have solid mounts) and transmission mount play a huge role in case breakage"

He also talks about a solid cast aluminum converter cover w/ strut arms used in some 4X4

1) do other use a solid cover to strengthen, who has them?
2) solid or poly tranny mount?
3) any other issues I am not looking at?

car weight 3900 - 4100 bout 500 HP

Any other info or input would be appreciated. This forum with Billy Nees, Mark Y ect have really helped me with this build, just want to say thanks again. Don't forget, this not a "dime rocket" , more like a "quarter rocket" so I want to stay away from somebody going through it plus a new tranny for now. ( need to get trailer, ect )

Thanks for any help.
Will Lamprecht Div 1 NHRA 65 impala I/SA 2016 debut!

GUMP · 12-21-2015, 12:02 PM

I wouldn't be afraid of hurting the case at that HP. Poly transmission mount for sure.

Jim Kaekel · 12-21-2015, 12:20 PM

Most TH-350 4WD cases used the special cast aluminum dust cover that helped strengthen the case, but you probably don't need it since you don't have a big, heavy transfer case hanging off the back of the trans. I would use a stock rubber trans. mount with stock engine mounts and a torque strap on the left front of the engine. If you want to help prevent case breakage, make or buy a brace that connects the boss on the right side of the bellhousing to the boss at the rear that's right in front of the tailhousing. I broke several bellhousings over the years prior to installing a brace. That's my .02.

Eman · 12-21-2015, 12:35 PM

Rubber mount for sure. Case will crack near cooler lines if stressed, only case I cracked was with a frt. motor plate and only a trans mount and the case was trimmed of tabs which weakened it. If you pull the pump and the input shaft it's easy to ck for the 36 element sprag if you're concerned. I ran with only a hardened race for years with no failures. Be gentle with 2nd gear and you'll have no problems. Start burnout in 2nd and shift to 3rd quickly. Don't ever come out of burnout in 2nd and shock it by having the tires grab.

ken robinson · 12-21-2015, 01:03 PM

The GM cases on all the glides & TH are not best castings , broke a few over the years . I run solid engine mount & rubber trans mount .1 bolt cross member to rubber mount . The 2-3 burn out works . Tire shake/spin can destroy parts . We run 350s in both cars .Your car has a full frame like Bob kingswood wagon . You'll be ok. Sometimes you just get a pour case/core . Driveshaft balance-ing not to be over looked too . See you at Lebanon ...

impstocker · 12-21-2015, 02:29 PM

Want to thank everbody for great advice. I am going to fabricate that brace today. I will continue to use the solid motor mounts with a poly tranny mount with 1 bolt. Yes Ken full frame also solid body mounts with 8 point roll bar welded through to frame plus some other gussets ect. No flex in frame and body.

Believe it or not I never raced a "real race car" with an automatic so the info on the 2-3 burnouts i never knew.

Will Lamprecht 65 imp I/SA

impstocker · 12-21-2015, 02:33 PM

Yes ken, I will be using the driveshaft which was built and balanced that I had in my 68 Impala. I would spin that to 7200. Had to find a place that would do it, most shops said to long would not do it!

Will

ss3011 · 12-21-2015, 03:08 PM

Another good upgrade is to install a 4L65 lo roller clutch assembly/support. This part is made of nodular iron, instead of a normal 350 which was gray iron , and the rollers were slightly wider. It will handle much more torque than a 350 roller clutch.

Dave Ribeiro · 12-21-2015, 07:43 PM

Make sure you talk to Jack Sepanek, he uses a torque strap on most of the T-350 & M-200's ... They are adjustable & work very well .... The other
thing to check into is JW bell-housing, used by lots of Stk / S/S racer's !!!!
Jack, can also help you with those ( JW bell-housings ) Good Luck with your project in 2016...

ken robinson · 12-25-2015, 02:14 PM

Daves wright the ultra bell can be used & I save one trans case which had alot of work im it already . Jack did say the bell it one of the week points .

12-21-2015, 11:08 AM	#1
impstocker Member Join Date: Dec 2008 Location: Wingdale, NY Posts: 302 Likes: 27 Liked 54 Times in 16 Posts	TH350 Strength I am finishing up my 1965 Impala 396/325 Stocker mocking up the motor with TH350 intalled in car. In previous post I mention the tranny has been in storage since 2002, I originally going to use in the 68 Impala I ran. (ran a stick in that one) The only thing I remember was I did get a 2.75 first gear plus a manual valve body. I don't even remember who built it except I think it was somebody in North Carolina. I finally did drop the pan last week, everything was clean (tranny has never been run) plus has a ATI valve body. I don't know if it has the 36 element sprag, but having it built they knew it was going into a race car, back then I had more $ so for now I can assume it has it. I remember it was around $900 in 2002. I like doing my own work plus lots of info, in reading Cliff Ruggles "GM Turbo 350" book he says: "the TH400 case is stronger where it flares up to the bellhousing area. I have seen a good number of TH350 break at this location, but all of those were being used in drag racing with high HP plus traction. Pinion angle, engine mounts (I have solid mounts) and transmission mount play a huge role in case breakage" He also talks about a solid cast aluminum converter cover w/ strut arms used in some 4X4 1) do other use a solid cover to strengthen, who has them? 2) solid or poly tranny mount? 3) any other issues I am not looking at? car weight 3900 - 4100 bout 500 HP Any other info or input would be appreciated. This forum with Billy Nees, Mark Y ect have really helped me with this build, just want to say thanks again. Don't forget, this not a "dime rocket" , more like a "quarter rocket" so I want to stay away from somebody going through it plus a new tranny for now. ( need to get trailer, ect ) Thanks for any help. Will Lamprecht Div 1 NHRA 65 impala I/SA 2016 debut!

12-21-2015, 12:02 PM	#2
GUMP VIP Member Join Date: May 2002 Location: Shelby, NC Posts: 1,665 Likes: 1,709 Liked 1,732 Times in 418 Posts	Re: TH350 Strength I wouldn't be afraid of hurting the case at that HP. Poly transmission mount for sure.

12-21-2015, 12:20 PM	#3
Jim Kaekel VIP Member Join Date: Jul 2002 Location: Michigan Posts: 1,222 Likes: 134 Liked 498 Times in 104 Posts	Re: TH350 Strength Most TH-350 4WD cases used the special cast aluminum dust cover that helped strengthen the case, but you probably don't need it since you don't have a big, heavy transfer case hanging off the back of the trans. I would use a stock rubber trans. mount with stock engine mounts and a torque strap on the left front of the engine. If you want to help prevent case breakage, make or buy a brace that connects the boss on the right side of the bellhousing to the boss at the rear that's right in front of the tailhousing. I broke several bellhousings over the years prior to installing a brace. That's my .02. __________________ Jim Kaekel 3836 STK

12-21-2015, 12:35 PM	#4
Eman Member Join Date: May 2014 Location: E TN Posts: 442 Likes: 14 Liked 105 Times in 60 Posts	Re: TH350 Strength Rubber mount for sure. Case will crack near cooler lines if stressed, only case I cracked was with a frt. motor plate and only a trans mount and the case was trimmed of tabs which weakened it. If you pull the pump and the input shaft it's easy to ck for the 36 element sprag if you're concerned. I ran with only a hardened race for years with no failures. Be gentle with 2nd gear and you'll have no problems. Start burnout in 2nd and shift to 3rd quickly. Don't ever come out of burnout in 2nd and shock it by having the tires grab.

12-21-2015, 01:03 PM	#5
ken robinson Member Join Date: Dec 2001 Location: tomsriver nj Posts: 441 Likes: 37 Liked 164 Times in 69 Posts	Re: TH350 Strength The GM cases on all the glides & TH are not best castings , broke a few over the years . I run solid engine mount & rubber trans mount .1 bolt cross member to rubber mount . The 2-3 burn out works . Tire shake/spin can destroy parts . We run 350s in both cars .Your car has a full frame like Bob kingswood wagon . You'll be ok. Sometimes you just get a pour case/core . Driveshaft balance-ing not to be over looked too . See you at Lebanon ...

12-21-2015, 02:29 PM	#6
impstocker Member Join Date: Dec 2008 Location: Wingdale, NY Posts: 302 Likes: 27 Liked 54 Times in 16 Posts	Re: TH350 Strength Want to thank everbody for great advice. I am going to fabricate that brace today. I will continue to use the solid motor mounts with a poly tranny mount with 1 bolt. Yes Ken full frame also solid body mounts with 8 point roll bar welded through to frame plus some other gussets ect. No flex in frame and body. Believe it or not I never raced a "real race car" with an automatic so the info on the 2-3 burnouts i never knew. Will Lamprecht 65 imp I/SA

12-21-2015, 02:33 PM	#7
impstocker Member Join Date: Dec 2008 Location: Wingdale, NY Posts: 302 Likes: 27 Liked 54 Times in 16 Posts	Re: TH350 Strength Yes ken, I will be using the driveshaft which was built and balanced that I had in my 68 Impala. I would spin that to 7200. Had to find a place that would do it, most shops said to long would not do it! Will

12-21-2015, 03:08 PM	#8
ss3011 Senior Member Join Date: Feb 2002 Location: Southeast Michigan Posts: 885 Likes: 63 Liked 221 Times in 102 Posts	Re: TH350 Strength Another good upgrade is to install a 4L65 lo roller clutch assembly/support. This part is made of nodular iron, instead of a normal 350 which was gray iron , and the rollers were slightly wider. It will handle much more torque than a 350 roller clutch.

12-21-2015, 07:43 PM	#9
Dave Ribeiro VIP Member Join Date: Sep 2002 Location: Williamsburg, Va.---USA Posts: 1,827 Likes: 1,612 Liked 56 Times in 27 Posts	Re: TH350 Strength Make sure you talk to Jack Sepanek, he uses a torque strap on most of the T-350 & M-200's ... They are adjustable & work very well .... The other thing to check into is JW bell-housing, used by lots of Stk / S/S racer's !!!! Jack, can also help you with those ( JW bell-housings ) Good Luck with your project in 2016... __________________ Dave Ribeiro 1033 STK

12-25-2015, 02:14 PM	#10
ken robinson Member Join Date: Dec 2001 Location: tomsriver nj Posts: 441 Likes: 37 Liked 164 Times in 69 Posts	Re: TH350 Strength Daves wright the ultra bell can be used & I save one trans case which had alot of work im it already . Jack did say the bell it one of the week points .